The present invention relates to a naphthyridine derivative useful as a medicament, particularly as a type IV phosphodiesterase inhibitor.
Asthma is a respiratory disease which repeats wheeze and attack by the contraction of airway. The number of the patients has been increasing steadily and is predicted to further increase hereafter.
Xanthine derivatives such as aminophylline and theophylline and xcex2-stimulators such as procaterol are now mainly used as bronchodilator for the treatment of asthma.
The functional mechanism of these compounds is to alleviate contraction of airway smooth muscle by increasing intracellular cyclic adenosine 3xe2x80x2,5xe2x80x2-monophosphate (cAMP) concentration through the activation of an intracellular cAMP producing enzyme, adenylate cyclase, or the inhibition of a cAMP hydrolyzing enzyme, phosphodiesterase (PDE) in airway smooth muscle (Internal Medicine, 69, 207-214 (1992)).
It is known that increased intracellular cAMP concentration induces inhibition of the contraction of airway smooth muscle (Clin. Exp. Allergy, 22, 337-344 (1992), Drugs of the Future, 17, 799-807 (1992)), which is useful in improving conditions of asthma.
However, it is known that the xanthine derivatives express systemic side effects such as hypotension and cardiotonic action (J. Cyclic Nucleotide and Protein Phosphoxylation Res., 10, 551-564 (1985), J. Pharmacol. Exp. Ther., 257, 741-747 (1991)), and the xcex2-stimulators are apt to cause desensitization and, when the dosage is increased, generate side effects such as finger tremor and palpitation.
On the other hand, it has been revealed that PDE is divided into at least five different types of from I to V, and each of them has different distribution or function (Pharmacol. Ther., 51, 13-33 (1991)). Particularly, type IV PDE does not act upon cyclic guanosine 3xe2x80x2,5xe2x80x2-monophosphate (cGMP) but specifically hydrolyze cAMP among nucleotides, and its presence is recognized in both of airway smooth muscle and infiltrating cells.
Also, it has been reported that type IV PDE inhibitors show inhibitory action upon eosinophiles infiltration by antigens and platelet-activating factors in guinea pig (Eur. J. Pharmacol., 255, 253-256 (1994)) and inhibit liberation of detrimental proteins (MBP, ECP) from eosinophiles (Br. J. Pharmacol., 115, 39-47 (1995)). It has been also reported that they show inhibitory action upon the contraction of airway smooth muscle by contractile substances (histamine, methacholine, LTD4) (Br. J. Pharmacol., 113, 1423-1431 (1994)), inhibit production of IL-4, a cytokine which is said to deeply participate in asthma (J. Invest. Dermatol., 100, 681-684 (1993)), express inhibitory action upon the acceleration of vascular permeability in the airway (Fundam. Clin. Pharmacol., 6, 247-249 (1992)) and show inhibitory action upon airway hypersensitivity (Eur. J. Pharmacol., 275, 75-82 (1995)). Thus, it is expected that a type IV PDE inhibitor will become an asthma-treating agent having less side effects.
As compounds having type IV PDE inhibitory activity, a large number of compounds are known including naphthyridine derivatives. The present applicant has previously reported a naphthyridine derivative represented by the following formula in which the 4-position (R6) is a cyclic substituent such as an aryl, a heteroaryl or a cycloalkyl and the 3-position (R5) is unsubstituted or a substituted lower alkyl group (WO 96/06843). 
(wherein R5 represents a hydrogen atom or a lower alkyl group and R6 represents an aryl group having a substituent, a heteroaryl group having a substituent, a cycloalkyl group or an adamantyl group. See the reference for other details.)
The present inventors have conducted studies with the aim of providing a novel compound which efficiently and selectively inhibits type IV PDE and is useful for preventing and treating respiratory diseases such as bronchial asthma with less side effects and also of providing a medicament containing the same.
The inventors have further conducted extensive studies on compounds having inhibitory activity upon type IV PDE and, as a result, found that a compound in which a specific substituent (xe2x80x94Xxe2x80x94R6) is introduced into the 3-position of the compound previously reported (WO96/06843) is a novel compound and has a strong type IV PDE inhibitory action, as well as excellent oral absorbability and metabolic stability. Therefore, they have found that the compound is markedly useful as a type IV PDE inhibitor, thus resulting in the accomplishment of the invention.
Accordingly, the invention relates to a novel naphthyridine derivative represented by the following general formula (I) or a pharmaceutically acceptable salt thereof and a medicament containing the same as the active ingredient. 
(wherein each symbol has the following meaning;
R1: xe2x80x94R0, -a lower alkylene-cycloalkyl or -a cycloalkyl
R0: -a lower alkyl,
R2, R3, and R4: xe2x80x94H, xe2x80x94R0, -a halogen, -a lower alkylene-OH, -a lower alkylene-SH, -a lower alkylene-Oxe2x80x94R0, -a lower alkylene-Sxe2x80x94R0, -a lower alkylene-Oxe2x80x94COxe2x80x94R0, -a lower alkylene-Sxe2x80x94COxe2x80x94R0, xe2x80x94OH, xe2x80x94Oxe2x80x94R0, xe2x80x94Sxe2x80x94R0, xe2x80x94SOxe2x80x94R0, xe2x80x94SO2xe2x80x94R0, xe2x80x94NH2, xe2x80x94NHR0, xe2x80x94NR02, -a cycloalkyl, xe2x80x94COxe2x80x94R0, or xe2x80x94CHxe2x95x90Nxe2x80x94OR9, which may be the same or different from one another,
R9: xe2x80x94H, xe2x80x94R0 or -a lower alkylene-aryl,
R5: a cycloalkyl which may be substituted with a group selected from R10, a cycloalkenyl which may be substituted with a group selected from R10, a heterocyclic group which may be substituted with a group selected from R10, or phenyl which may be substituted with a group selected from R10,
R6: xe2x80x94OH, xe2x80x94OR7, xe2x80x94COOH, xe2x80x94COOR7, xe2x80x94CONH2, xe2x80x94CONHR7, xe2x80x94CON(R7)2, xe2x80x94Oxe2x80x94COR7, xe2x80x94Oxe2x80x94COOR7, xe2x80x94CHO, xe2x80x94COR7, xe2x80x94NH2, xe2x80x94NHR7, xe2x80x94N(R7)2, xe2x80x94NHCOR7, xe2x80x94N(R7)COR7, xe2x80x94NHSO2R7, xe2x80x94N(R7)SO2R7, xe2x80x94CN, xe2x80x94NHCOOR7, xe2x80x94N(R7)COOR7, xe2x80x94C(NH)NH2, xe2x80x94NHC(NH)NH2 or xe2x80x94N(R7)C(NH)NH2, or a group represented by the formula xe2x80x94Yxe2x80x94R8,
R7: a lower alkyl which may be substituted with a group selected from the group consisting of xe2x80x94OH, -phenyl, -a halogen, xe2x80x94OR0, xe2x80x94CO2H, xe2x80x94CO2R0, xe2x80x94NH2, xe2x80x94NHR0, xe2x80x94NR2, xe2x80x94NO2, xe2x80x94CN, and xe2x80x94COR0,
R8: a cycloalkyl which may be substituted with a group selected from R10, an aryl which may be substituted with a group selected from R10, or a heterocyclic group which may be substituted with a group selected from R10,
R10: xe2x80x94OH, -phenyl, -a halogen, xe2x80x94OR0, xe2x80x94CO2H, xe2x80x94CO2R0, xe2x80x94NH2, xe2x80x94NHR0, xe2x80x94NR02, xe2x80x94NO2, xe2x80x94CN or xe2x80x94COR0, or a group described in R7.
Y: a bond, xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94CON(R7)xe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COOxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(R7)xe2x80x94, xe2x80x94NHCOxe2x80x94, xe2x80x94N(R7)COxe2x80x94, xe2x80x94NHCOOxe2x80x94, xe2x80x94N(R7)COOxe2x80x94, xe2x80x94NHSO2xe2x80x94, or xe2x80x94N(R7)SO2xe2x80x94, and
X: a bond or a lower alkylene, or a lower alkenylene. The same shall apply hereinafter.).
Also, according to the invention, there is provided a medicament, particularly a type IV PDE inhibitor, which comprises the naphthyridine derivative or a salt thereof.
The following describes the invention in detail.
The term xe2x80x9clowerxe2x80x9d as used herein means a straight or branched hydrocarbon chain having from 1 to 6 carbon atoms and examples of the xe2x80x9clower alkylxe2x80x9d include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, and the like. Preferred is an alkyl having from 1 to 4 carbon atoms, and particularly preferred is methyl or ethyl. The xe2x80x9clower alkylenexe2x80x9d means a divalent group formed by removing any one hydrogen atom from the above xe2x80x9clower alkylxe2x80x9d and is preferably an alkylene having from 1 to 4 carbon atoms, particularly preferably methylene, ethylene or propylene. The xe2x80x9clower alkenylenexe2x80x9d means a group having one or more double bonds at any position in the xe2x80x9clower alkylenexe2x80x9d having two or more carbon atoms, and is preferably an alkenylene having 2 to 4 carbon atoms.
The xe2x80x9ccycloalkylxe2x80x9d is preferably a cycloalkyl having from 3 to 8 carbon atoms, particularly preferably cyclopropyl or cyclohexyl. The xe2x80x9ccycloalkenylxe2x80x9d is preferably a cycloalkenyl having from 5 to 8 carbon atoms, particularly preferably cyclohexenyl. The xe2x80x9carylxe2x80x9d means an aromatic hydrocarbon group having from 6 to 14 carbon atoms, preferably phenyl. The xe2x80x9cheterocyclic groupxe2x80x9d is a monocyclic to tricyclic heterocyclic group having from 1 to 4 heteroatoms selected from the group consisting of nitrogen atom, oxygen atom, and sulfur atom, which may form a bridged ring or a condensed ring with benzene ring. This heterocycle is preferably a five- to seven-membered saturated or unsaturated monocyclic heterocyclic group, and is particularly preferably pyridine, piperidine, morpholine, thiophene, thiazole, imidazole, tetrazole, pyrazine or piperazine.
The xe2x80x9chalogenxe2x80x9d means F, Cl, Br or I.
The term xe2x80x9cwhich may be substitutedxe2x80x9d means xe2x80x9cnot substitutedxe2x80x9d or xe2x80x9chas from 1 to 5 substituents which may be the same or different from one anotherxe2x80x9d.
The substituent in the xe2x80x9ccycloalkyl which may be substitutedxe2x80x9d, xe2x80x9ccycloalkenyl which may be substitutedxe2x80x9d, xe2x80x9cheterocyclic group which may be substitutedxe2x80x9d, xe2x80x9cphenyl which may be substitutedxe2x80x9d, and xe2x80x9caryl which may be substitutedxe2x80x9d is not particularly limited as long as it can used as the substituent of these rings for medicaments, particularly a type IV PDE inhibitor, but is preferably xe2x80x94OH, -phenyl, -a halogen, xe2x80x94OR0, xe2x80x94CO2H, xe2x80x94CO2R0, xe2x80x94NH2, xe2x80x94NHR0, xe2x80x94NR02, xe2x80x94NO2, xe2x80x94CN or xe2x80x94COR0, or a lower alkyl which may be substituted with a group selected from these groups.
The group (Xxe2x80x94R6) at the 3-position of the naphthyridine is preferably a group more hydrophilic than the alkyl group having the same carbon atoms. For example, X is preferably a bond or a lower alkylene and R6 is preferably xe2x80x94OH, xe2x80x94COOH, xe2x80x94COOR7, xe2x80x94Oxe2x80x94COR7, xe2x80x94NH2, xe2x80x94NHR7, xe2x80x94N(R7)2, xe2x80x94C(NH)NH2, xe2x80x94NHC(NH)NH2 or xe2x80x94N(R7)C(NH)NH2, or a group represented by the formula xe2x80x94Yxe2x80x94R8. R8 is preferably an aryl or heterocyclic group. These groups may be substituted with a group selected from the group consisting of xe2x80x94OH, -phenyl, -a halogen, xe2x80x94OR0, xe2x80x94CO2H, xe2x80x94CO2R0, xe2x80x94NH2, xe2x80x94NHR0, xe2x80x94NR02, xe2x80x94NO2, xe2x80x94CN, and xe2x80x94COR0.
The group (R5) at the 4-position of the naphthyridine is preferably a cycloalkyl, phenyl which may have a substituent at the 3-position, or the like. The substituent is preferably a halogen, a lower alkyl, or the like. The groups (R3 and R4) at the 5- and 6-position of the naphthyridine are each preferably a lower alkyl or hydrogen atom, more preferably hydrogen atom. The group (R2) at the 7-position of the naphthyridine is preferably -a lower alkyl, -a halogen, -a lower alkylene-OH, or a group represented by the formula xe2x80x94CHxe2x95x90Nxe2x80x94OH.
Among the compounds of the invention, particularly preferable compounds are the following compounds: 3-(2-amidinoethyl)-4-(3-chlorophenyl)-1-ethyl-7-methyl-1,8-naphthyridin-2(1H)-one, 4-(3-chlorophenyl)-1-ethyl-3-(2-guanidinoethyl)-7-methyl-1,8-naphthyridin-2(1H)-one, 4-cyclohexyl-1-ethyl-7-methyl-3-[2-1H-tetrazol-5-yl)ethyl]-1,8-naphthyridin-2(1H)-one, 4-(3-chlorophenyl)-1-ethyl-7-methyl-3-[3-(1H-tetrazol-5-yl)propyl]-1,8-naphthyridin-2(1H)-one, 4-(3-bromophenyl)-1-ethyl-7-methyl-3-[2-1H-tetrazol-5-yl)ethyl]-1,8-naphthyridin-2(1H)-one, 3-[4-(3-chlorophenyl)-1-ethyl-7-methyl-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl]propanoic acid, 3-(4-cyclohexyl-1-ethyl-7-methyl-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl)propanoic acid, 3-[4-(3-chlorophenyl)-1-ethyl-7-methyl-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl]benzoic acid, 3-[4-(3-chlorophenyl)-1-ethyl-7-(hydroxyiminomethyl)-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl]propanoic acid, 3-[7-chloro-4-(3-chlorophenyl)-1-ethyl-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl]propanoic acid, 3-[1-ethyl-7-methyl-4-(3-methylphenyl)-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl]propanoic acid, 4-(3-chlorophenyl)-1-ethyl-7-methyl-3-(piperidin-4-yl)-1,8-naphthyridin-2(1H)-one and 1-{2-[4-(3-chlorophenyl)-1-ethyl-7-methyl-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl]ethyl}piperidine-4-carboxylic acid, and salts thereof.
Depending on the kinds of substituents, the compounds of the invention may exist in the form of geometrical isomers and tautomers, and isolated forms or mixtures of these isomers are included in the invention.
Also, the compounds of the invention may have asymmetric carbon atoms in some cases, and (R) and (S) forms of optical isomers can exist based on these atoms. The invention includes all of these optical isomers in mixed and isolated forms.
Pharmacologically acceptable prodrugs are also included in the compounds of the invention. The pharmacologically acceptable prodrugs are compounds having groups which can be converted into certain groups of the invention such as NH2, OH and CO2H by solvolysis or under a physiological condition. Examples of the groups which form prodrugs include those which are described in Prog. Med., 5, 2157-2161 (1985) and xe2x80x9cPharmaceutical Research and Developmentxe2x80x9d (Hirokawa Publishing Co., 1990) Vol. 7 Drug Design 163-198.
The compounds of the invention may form acid addition salts or, depending on the kinds of the substituents, salts with bases. Such salts are pharmaceutically acceptable salts, and their illustrative examples include acid addition salts with inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid and phosphoric acid and organic acids such as formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, fumaric acid, maleic acid, lactic acid, malic acid, tartaric acid, citric acid, methanesulfonic acid, ethanesulfonic acid, aspartic acid and glutamic acid, salts with inorganic bases such as sodium, potassium, magnesium, calcium and aluminum and organic bases such as methylamine, ethylamine, ethanolamine, lysine and ornithine, and ammonium salts.
In addition, the invention also includes various hydrates, solvates and polymorphic substances of the compound (I) of the invention and salts thereof.
(Production Method)
The compound of the invention and pharmaceutically acceptable salts thereof can be produced by applying various known synthetic methods making use of the characteristics based on its fundamental structure or the kind of substituent. In that case, depending on the kind of functional group, it is sometimes effective from the production technical point of view to replace the functional group at the starting material or intermediate stage by an appropriate protecting group, namely a group which can be easily converted into the functional group. Thereafter, the compound of interest can be obtained by removing the protecting group as occasion demands. Hydroxyl group and carboxyl group can be exemplified as such functional groups, and the protecting groups described for example in xe2x80x9cProtective Groups in Organic Synthesis (2nd Ed.)xe2x80x9d edited by Greene and Wuts can be cited as such protecting groups, which may be optionally used in response to the reaction conditions.
(1) First Production Method 
(wherein L1 represents a leaving group. The same shall apply hereinafter.)
In this production method, the compound (Ia) of the invention is produced by reacting an aminopyridine derivative (II) with an acylating agent represented by the general formula (III) to obtain an amide derivative (IV), and then directly subjecting it to a ring-closing reaction.
Preferred examples of the leaving group represented by L1 include halogen atoms, acyloxy, carbonates such as alkyloxycarbonyloxy and organic sulfonic acid residues such as methanesulfonyloxy and p-toluenesulfonyloxy. Also, through the combination of a substituent on XR6 with L1, the general formula (III) may form an intramolecular or intermolecular acid anhydride (e.g., glutaric anhydride).
The reaction is carried out in an organic solvent inert to the reaction, selected from halogenated hydrocarbons such as dichloromethane, dichloroethane and chloroform; aromatic hydrocarbons such as benzene, toluene and xylene; ethers such as diethyl ether, tetrahydrofuran (THF) and dioxane; and N,N-dimethylformamide (DMF); or without solvent, under from cooling to heating. In carrying out the reaction, the aminopyridine derivative (II) and the acylating agent (III) can be used in equivalent amounts or one of them in excess amount, and it is sometimes advantageous for smooth progress of the reaction to carry out the reaction in the presence of an organic base (preferably, triethylamine, pyridine or 4-(N,N-dimethylamino)pyridine), an inorganic base (preferably sodium hydroxide or potassium carbonate) or a metal base (preferably, sodium hydride, sodium methoxide or potassium tert-butoxide).
In this production method, isolation of the amide derivative (IV) and its ring-closing reaction may be carried out stepwise. In that case, with regard to the conditions of solvent, temperature, base and so on, the same conditions as those mentioned above can be employed in each reaction.
(2) Second Production Method 
In this production method, a compound (Id) of the invention having amino group is produced from the compound (Ib) of the invention having a carboxyl group. The carbamate compound (Ic) obtainable as the intermediate is also a compound of the invention.
The compound (Ic) of the invention can be produced by reacting an isocyanate compound which is obtained by the Curtius rearrangement of an acid azide obtained by the reaction of a reactive derivative of a carboxyl group obtained from the compound (Ib), such as an acid anhydride, with an azide salt such as sodium azide, or by the diphenylphosphoryl azide (DPPA) method, or which is by Hofmann rearrangement of an primary amide produced from the compound (Ib) according to an conventional amidation reaction, with an alcohol compound.
The reaction is carried out in an organic solvent inert to the reaction, selected from halogenated hydrocarbons, aromatic hydrocarbons, ethers and DMF, or without solvent, under from cooling to heating. In carrying out the reaction, the alcohol compound can be used in an equivalent or excess amount based on the compound (Ib).
The compound (Id) of the invention is produced by subjecting the compound (Ic) of the invention to a removing reaction of a carbamate type amino group-protecting group described in the xe2x80x9cProtective Groups in Organic Synthesis (2nd Ed.)xe2x80x9d mentioned previously. This reaction may be carried out successively without isolating the compound (Ic), following the above reaction.
(3) Third Production Method
A compound having a carboxyl group on R8 of the compound (I) can be produced by hydrolyzing the trifluoromethyl group on R8.
The reaction is carried out in an organic solvent inert to the reaction, selected from halogenated hydrocarbons, aromatic hydrocarbons, ethers and DMF, or without solvent, in the presence of an acid (hydrochloric acid, sulfuric acid, or the like) or a base (sodium hydroxide, sodium methoxide, or the like) under from cooling to heating.
(4) Fourth Production Method 
In this production method, compounds (If), (Ig) and (Ih) of the invention are produced from a compound (Ie) of the invention through the above pathway.
The compound (If) of the invention can be produced by dehydrating the compound (Ie) of the invention. A usual method of dehydration reaction can be used in the reaction, such as a method described for example in xe2x80x9cJIKKEN KAGAKU KOZA (4th Ed.)xe2x80x9d edited by The Chemical Society of Japan, vol. 20 (1992) (Maruzen).
The compound (Ig) of the invention can be produced by the reaction of the compound (If) of the invention with an azide salt such as sodium azide. The reaction is carried out in a solvent inert to the reaction, selected from halogenated hydrocarbons, aromatic hydrocarbons, ethers, alcohols such as methanol and ethanol, DMF and water, or without solvent, under from cooling to heating. In carrying out the reaction, the azide salt can be used in an equivalent or excess amount based on the compound (If), and it is sometimes advantageous for smoothly progressing the reaction to carry out the reaction in the presence of an acid (acetic acid, trifluoroacetic acid, triethylamine hydrochloride, hydrochloric acid, aluminum chloride or the like) or a base (pyridine, triethylamine, sodium hydroxide, potassium hydroxide, sodium methoxide, potassium tert-butoxide or the like).
The compound (Ih) of the invention can be produced by the reaction of the compound (If) of the invention with ammonia, an ammonium salt such as ammonium chloride or a metal amide such as sodium amide. It can also be produced by allowing an imidoyl chloride obtained by the reaction of the compound (If) with hydrogen chloride to react with an ammonium salt such as ammonium chloride. The reaction is carried out in a solvent inert to the reaction, selected from halogenated hydrocarbons, aromatic hydrocarbons, ethers, alcohols, DMF and water, or without solvent, under from cooling to heating and under from ordinary pressure to a forced pressure. In carrying out the reaction, the amination agent can be used in an equivalent or excess amount based on the compound (If).
(5) Fifth Production Method 
In this production method, a compound (Ii) is produced by a guanidino-forming reaction of the compound (Id) of the invention.
Examples of the guanidino-forming agent to be used in this reaction include cyanamide, amidino sulfate, 1-amidinopyrazole and S-methylisothiourea. The reaction is carried out in a solvent inert to the reaction, selected from halogenated hydrocarbons, aromatic hydrocarbons, ethers, alcohols, DMF and water, or without solvent, under from cooling to heating. In carrying out the reaction, the guanidino-forming agent can be used in an equivalent or excess amount based on the compound (Id), and it is sometimes advantageous for smoothly progressing the reaction to carry out the reaction in the presence of an acid (acetic acid, trifluoroacetic acid, hydrochloric acid, sulfuric acid or the like) or a base (pyridine, dimethylaminopyridine, triethylamine, sodium hydroxide, potassium hydroxide, sodium methoxide, potassium tert-butoxide or the like).
(6) Sixth Production Method 
(wherein Ra and Rb may be the same or different and each represents H or a group represented by R7 or R8. The same shall apply hereinafter.)
In this production method, a thiazole derivative (Ik) is produced from the compound (Ij) of the invention.
The aimed compound can be produced by reacting, with a thioamide (V), a bromo compound which is obtained by reacting the compound (Ij) with a brominating agent such as bromine, N-bromosuccinimide, or benzyltrimethylammonium tribromide, after isolation or without isolation. The reaction is carried out in a solvent inert to the reaction, selected from halogenated hydrocarbons, aromatic hydrocarbons, ethers, alcohols, acetic acid, DMF and water, or without solvent, under from cooling to heating. In carrying out the reaction, the compound (Ij) and the brominating agent or the bromo compound and the thioamide (V) can be used in equivalent amounts or one of them in excess amount, and it is sometimes advantageous for smoothly progressing the reaction to carry out the reaction in the presence of an acid or a base.
(7) Seventh Production Method 
In this production method, a chloro group is introduced into the pyridine ring of the compound (Il) of the invention.
The aimed compound can be produced by reacting a pyridine oxide compound obtainable by reacting the compound (Il) with an oxidating agent such as m-chloroperbenzoic acid, peracetic acid or hydrogen peroxide, with a chlorinating agent such as phosphorus oxychloride, phosphorus pentachloride or thionyl chloride after isolation or without isolation. The reaction is carried out in a solvent inert to the reaction, selected from halogenated hydrocarbons, aromatic hydrocarbons, ethers, alcohols, acetic acid, DMF and water, or without solvent, under from cooling to heating. In carrying out the reaction, the compound (Il) and the oxidating agent or the pyridine oxide compound and the chlorinating agent can be used in equivalent amounts or one of them in excess amount, and it is sometimes advantageous for smoothly progressing the reaction to carry out the reaction in the presence of an acid or a base.
The chloro group can be converted into various substituents by subjecting the compound (Im) of the invention obtained according to the present production method to usual ipso substitution reaction described in the publication of WO97/19078 and so on.
(8) Synthesis of Starting Materials 
(wherein, L2 represents a leaving group the same as L1 and M represents H or a metal salt. The same shall apply hereinafter.)
A starting compound (II) in which the substituent R2 and the pyridine ring are combined with a carbon-carbon bond and a starting compound (VI) having leaving groups on the 2-position and 6-position of the pyridine ring can be synthesized according to the method described on pages 19 to 21 of the publication of WO97/19078.
A starting compound (II) in which the substituent R2 and the pyridine ring are not combined with a carbon-carbon bond can be synthesized by subjecting the starting compound (VI) to ipso substitution reaction with an amine compound (VII) having R1 group and a nucleophilic reagent R2M (VIII), successively. The order of the ipso substitution reaction is suitably decided in consideration of the K substituents (R1NH and R2) and the leaving groups (L1 and L2). The reaction is carried out in a solvent inert to the reaction, selected from water, aromatic hydrocarbons, ethers and DMF, or without solvent, under from cooling to heating. It is sometimes advantageous for smooth progress of the reaction to carry out the reaction in the presence of an organic base, an inorganic base (preferably sodium hydroxide or potassium carbonate) or a metal base.
The compound of the invention obtained by each of the above production methods can be further converted into various compounds of the invention by subjecting the compound to each reaction of amidation, sulfonamidation, esterification, hydrolysis, alkylation, reduction of an ester, or nucleophilic substitution. Amidation, sulfonamidation, and esterification can be carried out according to methods described for example in xe2x80x9cJIKKEN KAGAKU KOZA (4th Ed.)xe2x80x9d edited by The Chemical Society of Japan, vol. 22 (1992) (Maruzen), hydrolysis according to a method described in the paragraph of deprotection of carboxyl group in the above xe2x80x9cProtective Groups in Organic Synthesis (2nd Ed.)xe2x80x9d, alkylation according to a method described for example in xe2x80x9cJIKKEN KAGAKU KOZA (4th Ed.)xe2x80x9d edited by The Chemical Society of Japan, vol. 20 (1992) (Maruzen), and reduction of an ester according to a method described for example in xe2x80x9cJIKKEN KAGAKU KOZA (4th Ed.)xe2x80x9d edited by The Chemical Society of Japan, vol. 20 (1992) (Maruzen). The nucleophilic substitution can be achieved by reacting a compound having an alkyl group substituted with OH with thionyl chloride or the like to form an alkyl chloride derivative or with methanesulfonyl chloride or p-toluenesulfonyl chloride to form an organic sulfonate ester, followed by reaction with a nucleophile. Alternatively, it can be also achieved by carrying out Mitsunobu reaction. The reaction is carried out in an organic solvent inert to the reaction, selected from halogenated hydrocarbons, aromatic hydrocarbons, ethers, and DMF, or without solvent, under from cooling to heating. It is sometimes advantageous for smoothly progressing the reaction to carry out the reaction in the presence of a base.
The reaction product obtained by each of the above production methods is isolated and purified as its free compound, salt or various solvates such as hydrate. The salt can be produced by carrying out a usual salt formation treatment.
The isolation and purification are carried out by employing usually used chemical techniques such as extraction, concentration, evaporation, crystallization, filtration, recrystallization and various types of chromatography.
Various isomers can be isolated in the usual way making use of the difference in physicochemical properties between corresponding isomers. For example, optical isomers can be separated by a general optical resolution method such as a fractional crystallization or chromatography. Also, an optical isomer can be produced starting from an appropriate optically active material compound.
Regarding the PDE inhibitory action, at least five types of from I to V have so far been known, and the compound of the invention has particularly excellent activity to inhibit type IV PDE and is therefore useful as an agent for preventing and/or treating respiratory diseases (e.g., bronchial asthma (including atopic asthma), chronic bronchitis, pneumonic diseases and adult respiratory distress syndrome (ARDS)) in which the type IV PDE participates. Particularly, it can be expected to be an agent for preventing and/or treating bronchial asthma.
In addition, the compound of the invention is also useful as an agent for preventing and/or treating other diseases in which involvement of the type IV PDE is known, such as those in which cytokine (IL-1, IL-4, IL-6 and TNF (tumor necrosis factor)) or the like are concerned (e.g., rheumatoid arthritis, ulcerative colitis, Crohn disease, sepsis, septic shock, endotoxin shock, Gram negative bacterial sepsis, toxic shock syndrome, nephritis, hepatitis, infection (bacterial and viral) and circulatory failure (heart failure, arteriosclerosis, myocardial infarction, stroke, or the like)). Also, since the compound of the invention is hardly metabolized by P450 drug metabolizing enzymes present in liver microsome and shows good oral absorbability and duration, it is useful as a long-acting drug having good pharmacokinetic profiles.
Availability of the compound of the invention was confirmed by the following tests.
Test Example 1. Type IV PDE Inhibitory Activity.
1) A solution containing type IV PDE was purified from rat ventricle muscle in the following manner. The heart excised from a male Wistar rat under ether anesthesia was washed with physiological saline and then the ventricle was separated. The thus separated ventricle was finely cut with scissors and suspended in a buffer A (20 mM Bis-Tris, 50 mM sodium acetate, 2 mM EDTA, 5 mM 2-mercaptoethanol, 2 mM benzamidene, 0.05 mM phenylmethylsulfonyl fluoride, pH 6.5) containing 1% PROTEASE INHIBITOR COCKTAIL For Mammalian Cell Extracts (SIGMA). Thereafter, the cells Were disrupted using Polytron and subjected to ultracentrifugation (100,000 G, 60 minutes, 4xc2x0 C.) to obtain a soluble fraction.
2) The resulting soluble fraction was applied to a 2.6xc3x9710 cm Q-Sepharose column equilibrated with the buffer A. Next, the column was washed with 1,200 ml of the buffer A to remove uncombined protein. The protein combined to the column was eluted using 750 ml of the buffer A containing a linear gradient sodium acetate solution of from 0.05 to 1.00 M, and 110 tubes each containing 7 ml fraction were recovered. The cAMP metabolizing PDE activity of each fraction obtained in the presence or absence of cGMP and calcium/calmodulin was examined. Each fraction which showed cAMP metabolizing activity and received no influence on the cAMP metabolizing activity by the presence of cGMP or calcium/calmodulin was used as a stock solution for the inspection of the type IV PDE inhibitory activity.
3) Each test compound in a predetermined concentration was allowed to undergo 10 minutes of the reaction at 30xc2x0 C. in a reaction mixture containing 40 mM Tris-HCl (pH 8.0), 5 mM magnesium chloride, 4 mM 2-mercaptoethanol, 1 xcexcM CAMP, 1 xcexcCi/ml [3H] cAMP and the type IV PDE stock solution. The reaction was stopped by adding xc2xd volume of 20 mg/ml polylysine coated yttrium silicate SPA beads (Amersham) suspension containing 18 mM zinc sulfate and 5 xcexcM 3-isobutyl-1-methylxanthine (IBMX) to the reaction solution, and the radioactivity was measured.
A concentration of test compound which inhibits 50% of the metabolic activity of type IV PDE was defined as IC50 and calculated for each compound.
By applying the above test method and the method described in WO 97/19078, the type I, II, III and V PDE inhibition activities were measured in the same manner.
As a result of the above inhibitory activity measuring test, it was confirmed that the compounds of Examples 2, 16, 21, 28, 38, 39, 40, 41, 43, 47, 61, 70, 77, 78, 79 and 80 have an IC50 value of 11 nM or less for the type IV PDE, including a compound having a potent activity of 0.002 nM.
Test Example 2. In vitro Drug Metabolism Test Using Liver Microsome
1) Human and rat liver microsome suspension (human microsome: Xenotech, rat microsome: Charles River) was diluted with 100 mM Na-K phosphate buffer (pH 7.4) to a protein concentration of 0.5 mg/ml. To a 100 xcexcl portion of this suspension were added 2 xcexcl of a test compound solution (a 10 xcexcg/ml acetonitrile solution), 500 xcexcl of 200 mM Na-K phosphate buffer (pH 7.4), 50 xcexcl of 1 mM EDTA-NaOH (pH 7.4) and 200 xcexcl of purified water, thereby preparing a substrate solution (concentration in the reaction solution: liver microsome (as the protein content) 0.05 mg/ml, test compound 20 ng/ml, 100 mM Na-K phosphate buffer, 0.1 mM EDTA-NaOH).
2) An NADPH production system was prepared by mixing 42 mg of NADP, 5 ml of 100 mM glucose-6-phosphatase (G6P) and 5 ml of 100 mM MgCl2, and adding 57 xcexcl of G6P dehydrogenase (about 1750 U/5 mg/ml) to the mixture. This was heated at 37xc2x0 C. for 5 minutes and then ice-cooled until its use.
3) A 900 xcexcl portion of the substrate solution was pre-incubated at 37xc2x0 C. for 5 minutes, and then 100 xcexcl of the NADPH production system was added thereto, following by reaction at 37xc2x0 C. for 10, 20 and 30 minutes. After termination of the reaction by adding 2 ml of ethyl acetate, the whole was ice-cooled. In this connection, a control sample was prepared by adding 100 xcexcl of the NADPH production system after adding 2 ml of ethyl acetate (0 minute reaction).
4) To the reaction solution was added 100 xcexcl of an internal standard substance having a predetermined concentration (an acetonitrile solution), 1 ml of 0.5 M phosphoric acid and 2 ml of ethyl acetate, followed by shaking for 10 minutes. After 10 minutes of centrifugation at 2,500 rpm, the ethyl acetate layer was separated and evaporated to dryness, and the residue was dissolved in 100 xcexcl of an HPLC mobile phase solvent. The test compound was eluted after about 12 minutes, and the internal standard substance after about 16 minutes, under the following conditions. (HPLC measuring conditions mobile phase: acetonitrile/20 mM ammonium acetate=2:3 (v/v), column: Discovery RP Amide C16, 4.6xc3x9735 mm (SUPELCO), flow rate: 0.8 ml/min., detection: UV 286 nm)
5) A ratio (residual ratio) of the peak height ratio after 10, 20 or 30 minutes of the reaction to the peak height ratio of each test compound in the control (peak height ratio to the internal standard substance) was calculated.
As a result of the above measuring test, it was confirmed that the compounds of Examples 2, 21, 28, 41, 43, 47, 77 and 79 are hardly metabolized by the P450 drug metabolizing enzyme present in the liver microsome. Test Example 3. Oral absorbability and pharmacokinetic profile evaluation test using type IV PDE inhibitory activity as the index
The following assay was carried out in order to evaluate oral absorbability and pharmacokinetic profiles of the type IV PDE-inhibiting compounds of the invention.
1) Each test compound suspended in purified water containing 0.5% methyl cellulose was orally administered to a seven-week-old male Fisher rat at a dose of 3 mg/kg. In the control group, a solvent (0.5% methyl cellulose in purified water, 3 ml/kg) was administered in the same manner. After the oral administration, blood samples were periodically collected in the presence of heparin from the caudal vein of each rat under ether anesthesia, and plasma was prepared in the usual way.
2) The plasma prepared from each rat administered with the test compound or solvent was added to the type IV PDE measuring system shown in the above Test Example 1 so as to be a final concentration of 0.1%, and the type IV PDE inhibitory activity was measured.
As a result of this test, it was revealed that the compounds of Examples 2, 21, 28, 41, 43, 47, 77 and 79 show good oral absorbability and metabolic stability in comparison with a comparative compound. (Comparative compound: 4-(3-chlorophenyl)-1-ethyl-7-methyl-2-oxo-1,2-dihydro-1,8-naphthyridine)
Based on the results of Test Examples 1 to 3, it was confirmed that the compound of the invention has type IV PDE inhibitory activity, and thus it is evident that it is useful as an agent for preventing and treating diseases in which the type IV PDE participates.
The pharmaceutical composition containing one or two or more of the compounds of the invention or salts thereof as the active ingredient is prepared using carriers, excipients and other additives which are generally used in the preparation of medicaments.
The administration may be either oral administration in the form of, e.g., tablets, pills, capsules, granules, powders or liquids or parenteral administration in the form of, e.g., intravenous or intramuscular injections, suppositories, transdermal preparations, transnasal preparations or inhalations. The dose is optionally decided in response to each case, e.g., by taking symptoms, age and sex of each patient to be treated into consideration, but is usually approximately from 0.001 mg/kg to 100 mg/kg per day per adult in the case of oral administration, which is administered once a day or by dividing into 2 to 4 doses per day. Also, when intravenous administration is conducted due to the symptoms, it is administered once or several times a day generally within the range of from 0.001 mg/kg to 10 mg/kg per day per adult. Also, in the case of inhalation, it is administered once or several times a day generally within the range of from 0.0001 mg/kg to 1 mg/kg per day per adult, and in the case of spreading, it is administered once or several times a day within the range of from 0.0001 mg/kg to 1 mg/kg per day per adult.
The solid composition in the oral administration according to the invention is used in the form of, e.g., tablets, powders or granules. In such a solid composition, one or more active substances are mixed with at least one inert filler such as lactose, mannitol, glucose, hydroxypropylcellulose, microcrystalline cellulose, starch, polyvinylpyrrolidone or aluminum magnesium silicate. In the usual way, the composition may contain inert additives including a lubricant such as magnesium stearate and a disintegrating agent such as carboxymethylstarch sodium or a solubilization assisting agent. If necessary, tablets or pills may be coated with a film of sugar or a gastric or enteric coating substance.
The liquid composition for oral administration contains, e.g., pharmaceutically acceptable emulsions, liquids, suspensions, syrups and elixirs and contains a generally used inert solvent such as purified water or ethanol. In addition to the inert solvent, this composition may also contain auxiliary agents such as a solubilizing agent, a moistening agent and a suspending agent, as well as sweeteners, flavors, aromatics and antiseptics.
The injections for parenteral administration use include aseptic aqueous or non-aqueous liquids, suspensions and emulsions. Examples of the aqueous solvent include distilled water for injection and physiological saline. Examples of the non-aqueous solvent include propylene glycol, polyethylene glycol, a plant oil such as olive oil, an alcohol such as ethanol, and polysorbate 80 (trade name). Such a composition may further contain a tonicity agent, an antiseptic, a moistening agent, an emulsifying agent, a dispersing agent, a stabilizing agent and a solubilization assisting agent. These compositions are sterilized, e.g., by filtration through a bacteria retaining filter, blending of a germicide or irradiation. In addition, these may be used by firstly making into sterile solid compositions and dissolving them in sterile water or a sterile solvent for injection use prior to their use.
The invention is illustratively described with reference to the following Examples which, however, do not limit the scope of the invention. Methods for producing the starting compounds are shown in the following Reference Examples. In this connection, 3-(3-chlorobenzoyl)-2-ethylamino-6-dimethoxymethylpyridine was produced in accordance with the method described in Reference Examples 44 of the publication of WO 97/19078, and 3-substituted 2-ethylamino-6-methylpyridine derivatives such as 3-(3-chlorobenzoyl)-2-ethylamino-6-methylpyridine and 3-cyclohexanecarbonyl-2-ethylamino-6-methylpyridine were produced in accordance with the methods described in Reference Examples 45, 48 and 51 of the publication of WO 97/19078, respectively.